This paper provides a novel contribution on the relation between school performance and cheating behavior by analyzing a sample of 170 pupils in 10 primary schools located in the outskirts of Goma (Congo, DR). In two subsequent school years, children were administered a questionnaire that included a modified Dice Rolling Task (DRT) and a Dictator Game (DG), while information on their school performance was obtained through the collection of school reports. We analyze whether cheating (measured through DRT) could be explained by school performance (measured by Math and Total scores) and altruism (measured by DG) when controlling for individual (such as age, sex, previously recorded cheating attitudes) and background (such as class, school, interviewer) characteristics. Our results show that cheating is positively associated with school performance, suggesting a positive correlation between cognitive abilities and the occurrence of opportunistic lies. This relation is robust to the inclusion of altruism as an explanatory variable. We also show that, while pupils’ cognitive skills are a good predictor of cheating, the opposite does not hold. Finally, we give evidence that math-skilled children tend to cheat more when the reward from cheating is larger.